This invention relates generally to expansion joints and in particular to an apparatus and method for making resilient articles using recycled material, such as recycled vehicle tire rubber.
Environmental considerations have dictated the use of recycled materials in many different types of products. For example, many different types of paper and plastic products contain recycled materials. It is also known to use recycled material, such as recycled vehicle tire rubber, as a thermoset material to extrude relatively hard articles (i.e., articles having a shore A hardness of 70 or greater) as shown in U.S. Pat. No. 5,312,573. However, the process described in this patent is not suitable for manufacturing resilient articles such as expansion joints.
Expansion joints are typically interposed between structural members such as sections of concrete paving to accommodate expansion and contraction of the structural members between which the expansion joint is interposed. It is advantageous both from an environmental and cost perspective to be able to manufacture expansion joints using recycled material.
There is, therefore, a need for a cost effective apparatus and method to manufacture resilient articles, such as expansion joints, using recycled material.
In accordance with the present invention, a resilient article suitable for use as expansion joint material and method of manufacturing same using recycled material are provided. Predetermined amounts of recycled thermoset material and thermoplastic binder are mixed and heated to achieve a mixture having a predetermined density. The mixture is then extruded into a die from which the mixture emerges at approximately the desired thickness of the finished article. The mixture then enters a calibrator, which more precisely adjusts the thickness of the mixture. The mixture is then cooled and cut to the dimensions desired for the finished article.
In accordance with a feature of the invention, an extruder is provided having a mixing chamber containing a rotatable screw member and a heating device operatively associated with the mixing chamber. Rotation of the screw member at a predetermined rate draws the mixture through the chamber and further mixes the thermoset and thermoplastic materials with air in the mixing chamber.
In accordance with another feature of the invention, the die has a heater operatively associated therewith for maintaining the mixture at a relatively uniform density consistent with the desired thickness of the finished article.
In accordance with yet another feature of the invention, the calibrator maintains the desired thickness of the mixture as it begins to cool.
In the preferred embodiment, the thermoplastic binder is waste polyethylene material and the thermoset material is ground vehicle tire rubber with the fabric and metal removed. To provide a finished article suitable for use as an expansion joint, the mixture is preferably comprised of about 80% thermoset material and about 20% thermoplastic binder, by weight.